Chapter 18 The Urinary System
Introduction Maintains homeostasis Organs Removes and restores solutes and fluids Organs Two kidneys: main filtering organs, produce urine Two ureters One bladder One urethra
Introduction (cont’d.)
Functions of the Urinary System
Functions of the Urinary System (cont’d.) Excretion: nitrogenous, drugs and toxins Maintaining blood volume and concentration Balance of water and dissolved salts pH regulation Balance of hydrogen ions
Functions of the Urinary System (cont’d.) Blood pressure maintenance Renin Erythrocyte concentration Erythropoietin: stimulates red blood cell production Vitamin D production Calciferol
The External Anatomy of the Kidneys
The External Anatomy of the Kidneys (cont’d.) Paired organs that are reddish in color About the size of a closed fist Located just above waist Between parietal peritoneum and posterior wall of abdomen Referred to as retroperitoneal
The External Anatomy of the Kidneys (cont’d.) Hilum: passage area for ureters, vessels, nerves Surrounding layers Renal capsule: innermost, barrier Adipose capsule: middle, protection Renal fascia: outer, anchors kidney
The Internal Anatomy of the Kidneys
The Internal Anatomy of the Kidneys (cont’d.)
The Internal Anatomy of the Kidneys (cont’d.) Medulla: inner area Renal pyramids: tips point inward Cortex: outer area Cortical material between pyramids Cortex and renal pyramids contain nephrons
The Internal Anatomy of the Kidneys (cont’d.) Nephrons: functional units of the kidney Minor calyx Funnel shaped, collects urine from pyramid ducts Major calyces: formed from minor calyces Join to form renal pelvis Renal pelvis narrows to form ureter
The Anatomy of the Nephrons
The Anatomy of the Nephrons (cont’d.) Nephron: microscopic renal tubule Bowman’s glomerular capsule: double-walled globe Podocytes: innermost layer Parietal layer: outermost layer Endothelial-capsular membrane: filter
The Anatomy of the Nephrons (cont’d.) Renal tubule Proximal convoluted tubule Descending limb, loop and ascending limb of Henle Distal convoluted tubule Collecting ducts
Blood and Nerve Supply to the Nephrons
Blood and Nerve Supply to the Nephrons (cont’d.)
Blood and Nerve Supply to the Nephrons (cont’d.) Renal arteries: transport 1200 mL of blood per minute Interlobar arteries Arcuate arteries Interlobular arteries Afferent arterioles divide into glomerular capillaries
Blood and Nerve Supply to the Nephrons (cont’d.) Efferent arterioles Peritubular capillaries Interlobular veins drain into arcuate vein Interlobar veins Renal veins
Physiology of the Nephrons
Physiology of the Nephrons (cont’d.) Functions Control blood concentration and volume Regulate blood pH Remove toxins from blood Stimulate red blood cell production
Physiology of the Nephrons (cont’d.) Urine formation Glomerular filtration Tubular reabsorption Tubular secretion Urine: 95% water, urea, uric acid, electrolytes 56 mL an hour is normal 30 mL an hour indicates possible kidney failure
The Ureters: Anatomy and Function
The Ureters: Anatomy and Function (cont’d.) Extensions of the renal pelvis Connect to urinary bladder Function: transport urine to urinary bladder Urine movement Peristalsis, gravity, hydrostatic pressure
The Urinary Bladder and the Micturition Reflex
The Urinary Bladder and the Micturition Reflex (cont’d.) Urinary bladder held in position by peritoneum Trigone: region between openings of ureters and urethra Detrusor muscle: three-layered smooth muscle Internal urinary sphincter: involuntary control
The Urinary Bladder and the Micturition Reflex (cont’d.) Micturition: expulsion of urine from bladder External urinary sphincter: voluntary control Bladder capacity 700-800 mL 200-400 mL: conscious of need to urinate Stretch receptors initiate micturition reflex
The Urinary Bladder and the Micturition Reflex (cont’d.) During urination Detrusor muscle contracts Muscles of pelvic floor and abdominal wall contract External urinary sphincter relaxes and urine moves from bladder to the outside
The Urethra: Male and Female Positions
The Urethra: Male and Female Positions (cont’d.) Urethra: connects bladder to the outside Females Lies directly posterior to pubic symphysis Located in wall of vagina 3.8 cm long Between clitoris and vaginal opening
The Urethra: Male and Female Positions (cont’d.) Males 20 cm long Passes through prostate gland and penis Opens at tip of penis Transports urine and semen
Animation – Urine Formation This animation presents an overview of how urine is formed [Insert Urine Formation.swf] Needs Animation introductory text and link
Summary Discussed the functions of the urinary system Described the internal and external anatomy of the kidney Discussed the structure and function of the nephron Discussed micturition and the role of the ureters and urinary bladder